disorders. The evidence regarding association is drawn from occupational and other studies in which subjects were exposed to a variety of herbicides and herbicide components.
In VAO, the committee was concluded that there are no definitive studies to determine whether exposure to dioxin or related herbicides is associated with CNS motor/coordination problems. However, follow-up of veterans and, to a lesser extent, environmental observations suggest that motor and coordination difficulties should be assessed further in exposed subjects. It was determined that longitudinal assessments of motor and coordination problems are warranted in exposed subjects, especially those with high exposure, such as the National Institute for Occupational Safety and Health cohort studied by Fingerhut et al. (1991). Vietnam veterans represent the most systematically evaluated group with chronic TCDD exposure, and the findings in this group suggest that CNS disorders may focus on the subtle clinical area of coordination and abnormal involuntary movement disorders. Since this area is a specific subspecialty of neurology, future evaluations should involve specialists in this field. Internationally accepted scales for movement disorders have been developed, and these scales should be used in future studies of such problems.
In addition to assessments that capture the disability related to any objective findings, VAO also stressed that in the past decade an increasing concern—unrelated specifically to the question of TCDD and the CNS—has developed scientifically over the possible link between Parkinson's disease and chemicals used as herbicides and pesticides (Semchuk et al., 1992). It was suggested that as Vietnam veterans move into the decades when Parkinson's disease becomes more prevalent, attention to the frequency and character of new cases in exposed versus nonexposed individuals may be highly useful in assessing whether dioxin exposure is a risk factor for eventual Parkinson's disease.
No new data directly addressing this topic have been published since VAO. There is, however, a persisting concern about the role of herbicides and pesticides in the pathogenesis of parkinsonism (Semchuk et al., 1993; Butterfield et al., 1993; Golbe, 1993). Using multivariate statistical methods, occupational herbicide use was the third highest predictor of eventual Parkinson's disease risk in the study by Semchuk et al. (1993). Butterfield et al. (1993) examined occupational and environmental factors associated with disease risk in patients with early-onset Parkinson's disease, comparing the findings to a control group. Parkinson's